Harnessing (roots and) soil biology. John Kirkegaard CSIRO Plant Industry

Transcription

1 Harnessing (roots and) soil biology John Kirkegaard CSIRO Plant Industry

2 What is soil biology?

3 Conservation farming - principles Minimum mechanical soil disturbance Permanent soil cover (crop or mulch) Diverse crop and pasture species

4 Improving productivity of modern, no-till farming Adoption is driven by Erosion control, water conservation Labour, machinery, fuel savings Timeliness of operations Soil health benefits Improved productivity Llewellyn et al, (2012) Field Crops Research 132,

5 The new environment for roots to perform Understanding Laboratory Disturbed soil Undisturbed soil Farming systems

6 Root hair Wheat root rhizosphere 500 m Image with cryo-scanning microscope, Watt et al., 2005

7 Long-term study at Harden (25 years) No-till/Retain vs Cultivate/Burn Wheat-Break crop m x 6 m (4 replicates) Yield gain 0.5 Yield diff (RDD-BC) (t/ha) HARDEN WAGGA Yield loss Improvements in soil parameters Good establishment Growing season Poor early rainfall vigour (mm) and yield Kirkegaard (1995), (unpublished)

8 Improving productivity in no-till Reducing impact of Rhizoctonia in no-till systems Understanding biological suppression in soil VVSR Gupta Strategies to improve productivity in intensive cereal systems Why do some varieties perform better? Michelle Watt Improving organic-matter build-up in stubble retention Limit may be nutrients rather than carbon input Clive Kirkby Investigating compatibility of livestock in no-till systems Impacts of sheep on soil and water use Hunt, Kirkegaard, Bell

9 Poor early vigour - biological constraints Intact soil cores from field No-till Cultivate No-till Fumigate (Kirkegaard et al, 1997; Simpfendorfer et al, 2002)

10 Inhibitory bacteria on root tips in no-till soil Pseudomonas per mm root (x 10 3 ) Cultivated soil Fast growing roots (Watt et al 2005, 2006) No- till soil Slow growing roots 0 Cultivated No-till

11 Options to improve crop vigour in no-till Encourage rapid root growth Sow early into warm soil Disturb the soil below the seed using deep points Select vigorous variety (Watt et al 2005)

12 Strategic tillage makes good sense Farmers adopt flexible approach to no-till < 5% practice multiple cultivation pre-sowing No-till adopters use cultivation on 30% area 88% use narrow points only (rather than discs) Discs used to sow ~30% cropped area GRDC 2010; Llewellyn et al 2012

13 Occasional tillage - irreparable soil damage..? Case specific, but evidence is contested Strategic tillage can resolve some issues weed, disease management, lime incorporation (23M ha acid soils) Recent study completed at Harden (Bissett et al, 2012) microbial biomass, community structure, diversity and function (rdna & rrna, TRFLP) diversity shifts across cropping cycle and treatments little evidence of long term effects on biomass or function

14 Stubble retention - the carbon conundrum... What s going on...? Soil carbon changes slow or absent Rumpel (2008) no change after 31 years Luo (2010) no difference in C at 69 paired sites Rumpel et al (2008) J. Soil Sci. Pl. Nutr. 8, 44-51; Luo et al (2010) Agric. Eco. Envir. 139,

15 Soil Organic Material where is the C? Light Fraction (dead but active) (up to 20%) Living (up to 10%) Soil Organic Matter or humus (very dead) (up to 95%)

16 Its soil organic matter NOT carbon... Dr Clive Kirkby PhD Target is stable organic matter (humus) NOT soil carbon Stable organic matter has a constant ratio of C:N:P:S Like bricks (C) and mortar (NPS) to build a stable brick wall Nutrients (not C) might limit humus formation from residues

17 Stable organic matter has constant CNPS ratio 500+ international and 100+ Australian soils 1000 lbs C requires 92 lbs N, 18 lbs P, 14 lbs S soils from various countries 105 Australian soils collected from four of the five mainland states 531 soils from various countries 105 Australian soils collected from four of the five mainland states 12 C:N r 2 =0.93 C:S r 2 =0.85 Total soil C (%) Total soil N (%) Total soil S (%) Kirkby et al (2011) Geoderma 162,

18 Nutrients increase C-sequestration from residue Humus Carbon carbon (%) % Soil + stubble + supplementary nutrients Soil + stubble Laboratory incubation study (Harden soil) error bars are SE (7 x 3-month cycles) Leeton 5 t/acre wheat straw + nutrients NPS 5 t/acre wheat straw Incubation cycle Kirkby et al (2012) Repeated addition of 5 t/acre wheat straw (3 monthly)

19 Losing old soil C while making new carbon 5 t/acre equivalent C13-labelled straw added single cycle Chane in carbon (mg kg soil -1 ) new C gained old C lost net change -7% % % Harden error bars are SE soil alone (control) soil + straw soil + straw + nutrients Soil only Soil + Straw Soil + Straw + Nutrients NPS Kirkby et al (2012)

20 Buntine sand + stubble incubation (5 weeks) Clive Kirkby (PhD)

21 It works in the field Harden field site We mulch the stubble then Add granular fertiliser to one plot Incorporate stubble No fertiliser on adjoining plot + _ + _

22 Humus-C increase of 7.5 t/ha after 3 years to 1.6 m Carbon (t/ha) Depth (10 cm increments) total C t/ha % of C is below 30 cm stubble + nutrients stubble

23 Implication hidden cost of C-sequestration Every 1 tonne of C-sequestered requires Nutrient Amount (kg) Approx price/kg nutrient Approx Cost ($) N P S $215 Australian government currently values CO 2 at ~$23 / tonne this equates to $84 per tonne of C

24 Implications of nutrient ratios to build SOM... C sequestration limited by nutrients, not C in no-till systems Nutrient management in no-till (spray onto residue?) Is strategic tillage necessary to sequester C from residues? Nutrient-use efficiency vs C-sequestration? Implications for: manures, cover-crops, biochar, municipal wastes etc...

25 Crop and pasture sequence

26 Important biological impacts of legume-based pastures kg of shoot N fixed per tonne of legume biomass produced at least 40% of N in cereals derives directly from previous legume N high input of labile C and N in plant and organic animal residues pasture increases organic carbon (~ 0.15% per year for 5 year) improves soil structure (aggregate stability increase 5-10%/yr)

27 Broadleaf rotation crops (legumes, canola) 20% (0.5 t/ha) yield benefit Water and nutrient efficiency Disease control (root and stubble borne) Weeds (control of grass weeds) Nitrogen Legumes (+20 to 50 kg/ha N) Residues easy to retain Kirkegaard et al (2008) Field Crops Research Seymour et al (2012) Crop and Pasture Science

28 Root exudates, soil biology and crop growth HUP- legumes H 2 released into soil (1500 gallons/ha/day) Growth-promoting bacteria (Peoples et al, 2008) White lupins Citrate release Improves P availability (Hocking 2001) Brassicas Isothiocyanates Pathogen suppression (Kirkegaard et al, 2008 )

29 Not all break crops are equal 4.00 Yield (t/ha) Wheat Oats Linseed Canola Mustard Previous crop Kirkegaard et al (2008) Field Crops Research

30 Biofumigation isothiocyanates from canola roots 2 cm GFP-labelled fungus Inside canola root glucosinolates Myrosinase enzyme Isothiocyanates (ITCs)

31 Dale Gies, Moses Lake potato disease control USA Pacific Northwest 35,000 ha green manure mustard Mustard green manure replaced Metham sodium Diseases managed Verticillium wilt Sclerotinia Rhizoctonia Streptomyces Nematodes Yield/quality maintained $US 169/ha saving Wind erosion control Increased water infiltration Improved soil organic matter CO 2 saving 2t C/ha/yr (1.0 mill km by plane) Andy McGuire WSU (2004); Dale Gies (2004)

32 But...intensive cereals dominate (64 to 80%) Why cereals? easy to manage, market - low risk more residues for cover/grazing New technology helps disease resistance, soil/seed fungicides, soil DNA testing new precision inter-row sowing, herbicide options Yield penalties persist (5-10%) in absence of obvious disease, N or other known factors evidence for bacterial involvement worth $200M pa

33 No-till root environment...not all good! Pore in no-till soil Live wheat crop roots Dead roots from preceding crop Hard soil no roots (Watt et al., 2005; ME McCully, images) 5 mm

34 Microbial succession on old and new roots Last year s dead roots Current roots Actinomycetes Cryo-scanning EM courtesy: Margaret McCully Watt et al (2005) Carbon Sugars Phenolics Acids Signals

35 Can rotating wheat varieties help? Shoot dry weight increase (% Janz on Janz) wheat Janz H45 V18 Intact core studies cereal Janz Janz Janz Janz Janz H45 H45 H45 H45 H45 Vig18 Vig18 Vig18 Vig18 Vig18 Janz H45 Vig18TriticaleOats Janz H45 Vig18TriticaleOats Janz H45 Vig18TriticaleOats

36 Recent study on bacterial succession Two-year wheat-wheat field study Plating, T-RFLP, Pyrosequencing Time (2 seasons) Variety (2) Soil type (2) Position (rhizoplane, rhizosphere, soil) Outcomes Donn et al, 2012 (in preparation) Position (space) and root age (time) significant determinants of populations Season, soil type, previous crop, current genotype minor determinants Inconsistent effects on growth and yield

37 Changes in microbe populations across sequence Year 1 wheat Year 2 heat 0.01 mm 5 mm Mixture young and dead roots Bacteria labelled with DNA probes Young wheat root Dead wheat root

38 Assessment of the wheat root soil microbiome Phylum Class Order year1 year2 TB Actinobacteria LB TB Alpha-proteobacteria LB Rhizoplane Rhizosphere (TB) (LB) g p % V1 R1 S b V2 V1 R1 V2 unclassified Bacteroidetes Acidobacteria Chloroflexi TM7 Firmicutes Proteobacteria Actinobacteria other Streptomycetaceae Microbacteriaceae unclassified Rhizobiaceae Caulobacteraceae Bradyrhizobiaceae The Challenge How does community Sphingomonadaceae unclassified succession Micromonosporaceae Kineosporiaceae Nocardioidaceae α-proteo incertae sedis Pseudonocardiaceae Geodermatophilaceae Mycobacteriaceae Phyllobacteriaceae Hyphomicrobiaceae Acetobacteraceae unclassified Micrococcaceae Other Other influence crop performance? Proteobacteria nutrient availability growth promotion disease suppression Can the microbiome be managed for agronomic benefit? 0 0 Oxalobacteraceae Burkholderiales incertae sedis γ δ β α Burkholderiaceae Comamonadaceae unclassified Neisseriaceae Other Bacteroidetes Beta-proteobacteria Gamma-proteobacteria Change in community composition with time and root compartment 20 0 Flavobacteriaceae Sphingobacteria_unclass Cytophagaceae Cryomorphaceae Other Sphingobacteriaceae Chitinophagaceae unclassified Bacteroidetes_incertae_sedis 20 0 Pseudomonadaceae Xanthomonadaceae γ_unclass Enterobacteriaceae Sinobacteraceae Other

39 Soil biology and health... - Not everything that is important can be measured, and not everything that can be measured is important... Albert Einstien - 3

40 Roots for the future...weed suppressive? Wasson et al (2012) J. Exp. Bot. 63, Sorgoleone on sorghum root tips

41 New frontier - root-soil biology research Understanding Synergies from new root genetics precision placement novel input/formulations Lab Tilled No-till Farming systems Further gains in efficiency and productivity

42 Many colleagues, farmers and friends... Thank you CSIRO Plant Industry John Kirkegaard Contact Us Phone: or Enquiries@csiro.au Web: